Probing Ag nanoparticle surface oxidation in contact with (in)organics: an X‐ray scattering and fluorescence yield approach

Characterizing interfacial reactions is a crucial part of understanding the behavior of nanoparticles in nature and for unlocking their functional potential. Here, an advanced nanostructure characterization approach to study the corrosion processes of silver nanoparticles (Ag‐Nps), currently the most highly produced nanoparticle for nanotechnology, is presented. Corrosion of Ag‐Nps under aqueous conditions, in particular in the presence of organic matter and halide species common to many natural environments, is of particular importance because the release of toxic Ag⁺ from oxidation/dissolution of Ag‐Nps may strongly impact ecosystems. In this context, Ag‐Nps capped with polyvinolpyrrolidone (PVP) in contact with a simple proxy of organic matter in natural waters [polyacrylic acid (PAA) and Cl^? in solution] has been investigated. A combination of synchrotron‐based X‐ray standing‐wave fluorescence yield‐ and X‐ray diffraction‐based experiments on a sample consisting of an approximately single‐particle layer of Ag‐Nps deposited on a silicon substrate and coated by a thin film of PAA containing Cl revealed the formation of a stable AgCl corrosion product despite the presence of potential surface stabilizers (PVP and PAA). Diffusion and precipitation processes at the Ag‐Nps–PAA interface were characterized with a high spatial resolution using this new approach.     

Landau–Pomeranchuk–Migdal effect in a quark–gluon plasma and the Boltzmann equation

We show how the Landau–Pomeranchuk–Migdal effect on photon production rates in a quark–gluon plasma can be derived via the usual Boltzmann equation. To do this, we first derive the electromagnetic polarization tensor using linear response theory, and then formulate the Boltzmann equation including the collisions mediated by soft gluon exchanges. We then identify the resulting expression for the production rate with that obtained by the field-theoretic formalism recently proposed by Arnold, Moore and Yaffe. To illustrate the LPM effect we solve the Boltzmann equation in the diffusion approximation.     

Improved rejection of multiply scattered photons in confocal microscopy using dual-axes architecture

We perform Monte Carlo simulations to show that the dual-axes (DA) confocal architecture has superior rejection of multiply scattered photons in tissue to that of single axis. As a result, the DA configuration provides improved signal-to-noise ratio and dynamic range, and thus is sensitive to ballistic photons from deeper within tissue, features that are particularly useful for performing vertical cross-sectional reflectance images in tissue.     

The production and destruction of the C-related 969 meV absorption band in Si

Data are reported on the production of the 969 meV absorption line as functions of the carbon concentration and radiation dose in FZ and CZ silicon. With increasing dose of 2 MeV electrons the absorption first increases and then decreases. Simple equations are presented which describe the growth and decay. It is shown that, in favourable circumtances, carbon concentrations as low as 10¹⁴ cm⁻³ can be detected in silicon by means of the 969 meV absorption line. We verify that the 969 meV line anneals out at temperatures >500 K but may increase between 450 and 500 K. We show that the increase is largest in samples irradiated at room temperature to a small dose relative to the carbon concentration.     

Observation of large CP violation in the neutral B meson system

We present a measurement of the standard model CP violation parameter sin2 phi(1) based on a 29.1 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is fully reconstructed as a J/psi K(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psi K(L), or J/psi K(*0) decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2 phi(1) = 0.99+/-0.14(stat)+/-0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.     

On the projection and macphail constants ofl n p spaces

We prove that the projection and Macphail constants ofl _n ^p (1≦p≦2) are asymptotically equivalent ton ^1/2 andn ^−1/2 respectively. We also obtain some relations linking certain parameters of general finite dimensional real Banach spaces. This note is a part of the author’s Ph.D. Thesis prepared at the Hebrew University of Jerusalem, under the supervision of Prof. J. Lindenstrauss, to whom the author wishes to express his thanks and appreciation.     

Electrochemical methods for analysing and controlling charge transfer at the electrode–tissue interface

There have been rapid advances in the development of new materials for use in electrode–tissue interfacing. The development of conducting polymers, conducting hydrogels, carbon nanotubes, graphene and other conducting materials has provided a rich landscape for controlling charge transfer at the electrode–tissue interface and hence to monitor and manipulate cell behaviour. These materials have been used in tissue-engineered constructs to direct and control cell proliferation, growth and differentiation. However, their translation to clinical devices has been less successful. In this review, the use of electroanalytical techniques to develop an understanding of charge transfer at the electrode–tissue interface is discussed. In particular, the impact of solution and electrode conditions on charge injection capacity is demonstrated. The importance of standardised testing methods and the correlation of electrochemical and electrophysiological performance show the limitations of empirical studies and help define key electrode properties for clinical devices. The development of a sound theoretical basis for charge transfer at this increasingly important interface is being advocated to improve clinical outcomes and device lifetime and reduce power usage.     

Determination of work functions near melting points of refractory metals by using a direct-current arc

A direct-current arc in argon at atmospheric pressure was used to determine effective work functions of refractory metals, including tantalum, tungsten, molybdenum, and niobium. The procedure is experimentally advantageous because surface cleanliness of the specimen is not critical, high vacuum is not required, and the anode-cathode spacing is not critical. The experimental procedure involves striking an arc to a metal wire cathode to form a melted ball having an emitting area defined by its diameter. The literature melting point of the metal is taken as the emitting temperature. By using these parameters and the known arc current, effective work functions were calculated from the Richardson-Dushman equation. The calculated work functions agree with recommended handbook values to within about 0.1 V and have typical repeatabilities of 0.02 V. By varying the arc current, Richardson plots can be made over a temperature range from a few hundred degrees below the melting point to about 50° over the melting point of the test metal. A Richardson plot over this temperature range is presented for tantalum.     

Self-avoiding walk in five or more dimensions I. The critical behaviour

We use the lace expansion to study the standard self-avoiding walk in thed-dimensional hypercubic lattice, ford5. We prove that the numberc _n ofn-step self-avoiding walks satisfiesc _n ~A ⁿ , where is the connective constant (i.e. =1), and that the mean square displacement is asymptotically linear in the number of steps (i.e.v=1/2). A bound is obtained forc _n(x), the number ofn-step self-avoiding walks ending atx. The correlation length is shown to diverge asymptotically like (^––Z)^1/2. The critical two-point function is shown to decay at least as fast as x^–2, and its Fourier transform is shown to be asymptotic to a multiple ofk ^–2 ask0 (i.e. =0). We also prove that the scaling limit is Gaussian, in the sense of convergence in distribution to Brownian motion. The infinite self-avoiding walk is constructed. In this paper we prove these results assuming convergence of the lace expansion. The convergence of the lace expansion is proved in a companion paper.Supported by the Nishina Memorial Foundation and NSF grant PHY-8896163.Supported by NSERC grant A9351